Complaints that Facebook's app for iOS causes excessive iPhone battery drain date back a couple of years. But with renewed outcry from users and iOS 9's ability to monitorbattery usage, Facebook has admitted its app is a resource hog and issued an update to correct the problem.

"We found a few key issues and have identified additional improvements, some of which are in the version of the app that was released Friday," Facebook engineering manager Ari Grant wrote on the Facebook blog. According to Ari Grant, the problem was twofold: First, Facebook's app had something called 'CPU spin' in its code.

"A CPU spin is like a child in a car asking, 'Are we there yet? Are we there yet? Are we there yet?' with the question not resulting in any progress to reaching the destination. This repeated processing causes our app to use more battery than intended," wrote Grant in a public Facebook post.

"If you leave the Facebook app after watching a video, the audio session sometimes stays open as if the app was playing audio silently. The app isn't actually doing anything while awake in the background, but it does use more battery simply by being awake," wrote Grant.

Grant also pointed out that the excessive battery drain had nothing to do with how Facebook manages location, as some users have suspected. The new version of Facebook's iOS app, available in Apple's App Store, should be less of a battery hog for the iPhone.